1. Field of the Invention
This invention relates generally to a file guide and more particularly to a file guide for use in sharpening the cutting edge of a cutting tooth of a saw chain and for filing the corresponding depth gauge.
2. Description of the Prior Art
Saw chains of the type herein concerned have a plurality of cutters which are articulated in a well-known manner to the adjacent cutters of the saw chain. Each cutter has a body portion with a cutting tooth and a depth gauge in advance of the cutting tooth for limiting the depth of cut in a manner well known to those skilled in the art.
The cutting edge of each cutting tooth is normally sharpened by using a round file. A device for supporting a round file for sharpening cutting edges is shown in U.S. Pat. No. 2,737,830 to Silverson, et al.
A problem arises, however, when the cutting edge is sharpened since the outward projection of the cutting edge is reduced relative to the height of the depth gauge on the cutter. This reduces the cutting efficiency of the cutting edge. The efficiency can be restored by filing the depth gauge until the proper relationship between the respective heights is restored. However, the depth gauge must not be filed too much or the cutting edge will take too deep a cut and increase the likelihood of saw chain kickback.
A file guide for adjusting the relationship between the depth gauge and cutting edge of a cutting tooth is disclosed in U.S. Pat. No. 3,055,238 to Hazzard. Thus, the Hazzard patent discloses a combination file guide which rests on the tip of the cutting edge of the cutting tooth corresponding to the particular depth gauge to be filed and, therefore, the cutting edge tip is dulled which results in a loss of cutting efficiency. Furthermore, the Hazzard file guide is not angled to correspond to the incoming angle of the depth gauge which further decreases cutting efficiency.
U.S. Pat. No. 4,587,868 to Kuwica discloses a file guide for filing depth gauges which is angled to correspond with the incoming angle of the depth gauge. However, the file guide rests on the corresponding cutting edge tip, the use of the file guide dulls the cutting edge tip with consequent loss of cutting efficiency. In addition, the Kuwica file guide is cumbersome to use since it requires several pieces to align the file with the depth gauge.